A spin transfer torque MRAM (Magnetic Random Access Memory) using a perpendicular magnetization film for a recording layer is advantageous in order to decrease a write current and increase the capacity. A stacked film consisting of cobalt (Co) and platinum (Pt) each having a dense atomic plane has high crystal magnetic anisotropy of 107 erg/cm2, and can achieve a high magnetoresistive ratio (MR ratio) with low resistivity. Such stacked film is, therefore, receiving attention as a technique for achieving large scale integrated MRAM.
On the other hand, in terms of crystal structure, ruthenium (Ru) is used as an underlayer made of a CoPt alloy. The Ru underlayer increases the damping constant of a recording layer. This undesirably increases a write current. In a spin transfer torque MRAM using a perpendicular magnetization film, a write current increases in proportion with the damping constant, in inverse proportion with the spin polarizability, and in proportion with the area. A technique of decreasing the damping constant, increasing the spin polarizability, and reducing the area is necessary for decreasing the write current.